This invention relates generally to digital signal processing (DSP) and, more specifically, to methods and apparatus for generating motor drive signals for micro-electromechanical system (MEMS) gyroscopes.
To provide a motor drive signal for MEMS gyroscopes, a digital sinusoidal signal of frequency fo is generated by a numerically controlled dual-frequency oscillator (NCDFO). A command input to the oscillator is βo=cos(2πfoT), where fs=1/T is a clock frequency of the oscillator. The frequency fo varies with changes in βo. The digital sinusoidal signal serves as the input to a drive circuit which, in turn, provides an analog signal to a gyroscope drive motor. Because the above described gyroscope motor drive configuration is within a closed-loop control system, the destabilizing effect of time delay, and an attendant phase shift resulting from the time delay, will cause an operational issue to result.
One known attempted solution is to pass the NCDFO output signal through a digital-to-analog converter (DAC), whose output is passed through a low pass, anti-aliasing filter to smooth the analog gyro-drive signal. Unfortunately, the time delay introduced by the combination of these operations is too long to permit solid closed-loop operation. A digital-to-analog-conversion scheme with lower phase shift is clearly needed.